Ambient compensated time delay switch

ABSTRACT

A switch having a bimetal latch for locking a movable spring contact in closed circuit with a second contact, and a heating coil for activating the latch to release the spring contact. A second bimetal element engages and opposes the bimetal latch and thereby counteracts the torque developed in the bimetal latch by changes in the ambient temperature.

Ullitfld States I I i i 1151 3,702,454

Brown 1 51 Nov. 7, 1972 [s41 AMBIENT COMPENSATED TIME 3,559,140 1/1971Brown ..337/7s DELAY SWITCH 3,496,509 2/1970 Metcalf ..337/77 xInventor: Horace D. Brawn, Miami, Fla- LOl'CnZ X 31 Assisnee: MonmCorporation, Miami, Fla. Primary Examiner-Bernard A. Gilheany [22]Filed; Sept, 24, 1971 I Assistant Examiner-Dewitt M. Morgan [52] us. 01..J ..337/77, 337/78, 337/81, A swim hams metal latch a mmbe 337/101spring contact in closed circuit with a second contact, [511 1111. c1."110111 61/013, 110111 71/16 a heating activating the release [53] n w01 Search "337/37, 41, 56, 75 76, 77, the spring contact. A secondbimetal element engages 7 7 31, 96, 99 101, 27 341, 5 and opposes thebimetal latch and thereby counteracts 37 the torque developed in thebimetal latch by changes in the ambient temperature. v

[56] References Citerl I 3Clai ms,6Drawing Flgures UNITED STATES PATENTS3,569,887 3/1971. Brown; ..'.337/77 I VI I lmmcomsslmm DELAY'SWHEII Thisinvention" relates tolls." Pat. No. 3,569,887. Its main object is toprovidea more; effective means of compensating for extreme changes intheambient temis adversely affected. t 4 A further object of the present"invention" isto properature, wherein the' length of the -tirne delayinterval vide aydelayed' action switch of very simple structure,

v f FIG. 3 shows the relative position of the switch elementsintheONposition.

- FIG; 4 is a detail view illustrating. the latching action of .thedelay device after the switch has been manually turned to the OFFposition. I

FIG; 5 demonstrates in anotherdetail view the overriding position bf thetoggle whereby the latch is dis- A second birnetal element is rivetedto-terminal block 10, in juxtaposition withbimetal blade 1. Thefree'end"1 =7of'bimetall5 extends and isbentat 18 to engagethe latchside of bimetal bladel. The purpose of-the bimetal element"15 will be?detailed'in the final paragraphsof this'specification. a

' A cover plate, or'mounting yolte 30 is shown, FIG. 1

I having conventionalrnountingends 35, for installation in standard wallreceptacle boxes.

To turn the switch on, the toggle 28' is manually moved from the OFFposition shown in FIG. 1 to the ON position of-FIG'. 3. Movement-of saidtoggleto the ONposition rotates cam 29. against spring 19 forcingsaid-springdownward; thereby causingextension 16 to electrically engagecontact which is riveted at 5 to mounting block 10. Contact 23 iselectrically connected' to terminal 22 (via means not shown) to completean electric circuit between terminal spring 19 and terminal 22. Asspring 19 moves to the closed;cir-

cuit position, end traverses the angular surface 4 on latch 34 anddisplaces said latch from the path of movement of said end. When thespring 19 reaches its fully closed position, FIG. 3, the ,bimetalIspririgs back to its normal position and places latch 34 in the returnpath of movement :of end 7.In the fully ON position of FIG.

' cam'29 holds spring 19 down far enough so that the Placed and thedelay. interval is circumvented to. in-

stantly turn the switch off.

I FIG. '6 is a detail side view of the switch elements showing the comensating action of this invention.

Referring in greater detail to the drawing, in which like numeralsindicate like parts throughout theseveral views, the numeral 24; FIG.1", represents a nonconductive plastic case with its side will cut awayto reveal the intemal arrangement .of .the switch components. The

case 24 supports three terminals 13,22, and 19, in

slotted openings26, 25, and 27, respectively. Binder head screws 14,6,and 21 providea'convenient means of attaching external circuit wires tothe switch.

The terminal spring bends ninety degrees at 32, and extends through thecase 24 to engage the latch 34 on r the bimetal blade 1. The flexiblespring :19 pivots from the .open circuit position shown in FIG. '1 totheclosed circuit position visible in FIG..3.. 2

The shaft 3110f toggle 28 is cradled in the two bearings 38 in case 24,and pennits said toggle to pivot from thev position shown in FIGII tothe position illustrated in FIG. 3. A cam 29 on toggle 28 engages spring19.

The terminal 13 is rrigidly supported in the slotted opening 26 in case24, and is riveted at 8 to a nonconend 7 "does not engage latch 34.

Totum the switch off, the toggle 28'is manually moved to the OFFposition visible in FIG. 1. Cam '29 is thereby rotated. away from"spring 19, permitting said spring to pivot upward far-enough to bring.end 7 into engagement latch 34. Electrical continuity is establishedbetween: terminall9 .and terminal 13 via engagement'of end with latch34, causing current to flow throughcoil '2. The binietal blade I flexesaway from end 7 as a result of heat generated by the current flowingthrough coil 2. ,A sliding contact is'maintained between end 7-and latch3.4 as said latch is drawn away from theend 7 by the flexingofblade l.When'sufficient heat has'been generatedto flex the bimetal-l to theposition shown in FIG. 5, t he spring 1 9 will be ductivei terminalmounting block 10 within case.

The bimetal blade 1 is riveted at one end 1'1 to the mounting block 10,and a latch 34-is an integral partof said blade. Said latch 34 issituated in the path of movev rnent of. the end 7 on spring 19.

A coil of resistance wire 2 encircles the .bimetal 'l, and is connectedat one end 12' to the terminal 13. The

opposite end of said coil is connected to said bimetal at point 33. Whenend 7 engages latch 34, an electric circuit is completed from terminal19, through coil 2, to

terminal 13, and the resulting current flowing through said coilgenerates heat which causes the bimetal l to flex away from the end 7. Anonconductive sleeve 3 insulates bimetal 1 from coil 2.

released by latch and will return to the open circuit position of FIG.I. An interval of timelapses between the instant when the toggle 28 ismanually moved to the OFF position and the instant when spring 19 isreleased by latch 34. The length of the delay interval is determined bythe time required for coil 2 to generate the necessary heat? for flexingthe bimetal blade 1 sufficiently to-remove thelatch 34 fromthe returnpath of movement of end 7.

Another factor, however, imposes an undesirable effect upon the-lengthof the delay interval: the constantly changing ambient temperature. Whenthe surrounding temperature decreases, the bimetal blade 1 if notrestrained, will flex toward the end 7, and if it is restrained frommotion, it will build up force the direction of end 7 as a result of.the temperature drop.

The adverse flexure, or force build up, must first be counteracted, orovercome, before the desired directional motion can be obtained wherebythe switch is actuated. Consequently, when the switch is functioning ina below normal temperature environment, the heat generated by coil 2must first overcome the adverse torque already existing in blade 1before its normal functionbegins. I

. To cancel the effect of this adverse flexure, a second bimetal element15 is rigidly fixed to the terminal base at one end 36, and is orientedso that its temperature responsive flexure opposes that of bimetal l.The free end of bimetal is bent 17 to extend toward the free tion", theresulting opposite motion of the two units causes end 41 and end 18 toengage. A continued decrease in their common" temperature will serve tobuild up force in bothbimetal units, each one exerting force againstthe. other, and each unit thereby restraining the other against motion.The counteracting force of each ,bimetal unit against the other, due tothe engagement of end 41 with end 18, neutralizes the pulling force thatotherwise would cause the two ends of the respective bimetal units toflex away from each other.

In order to visualize the ambient temperature compensating action ofthis invention, let us assume that the environmental temperature isthirty degrees below zero F. When the toggle 28 is rotated to the OFFposition, FIG. 4, the end '7 of spring 19 engages'latch 34, therebyenergizing the coil 2. Because of the opposing stresses alreadydeveloped in bimetal l and bimetal 15 by the extremely cold environment,end 18 and end 41 will be firmly pressed'together. The heat produced inbimetal l by the current flowing in coil 2 immediately begins toneutralize the torque existing in blade 1. No heat, however, isgenerated in bimetal 15. The counteracting pull of bimetal l5v is,therefore still present, and continues toexert itself against bimetal l.The heat generated by coil 2 functions to flexbimetal l and latch 34 ina "direction to release end -7, while the-low ambient temperature causesbimetal 15 to flex in the same direction. The continued pulling force ofbimetal '15 against bimetal l], coupled with the heat flexture ofbimetal 1, results in the two bimetal units bending in the samedirection as shown in FIG. 6, thereby releasing end 7 to return to theopen circuit position. A heat shielding sleeve 20 isolates bimetal 15from the heat produced in coil 2.

The delay period may be avoided and the switch may be instantly turnedoff is desired. To accomplish this the toggle 28 must be manually movedto the overriding position shown in FIG. 5. The projection 9 is shown inthis view engaging the latch 34. Rotation of toggle 28 7 4 a a pullingaction against bimetal blade I. It will be obvious to anyone skilled inthe art of bimetal design that a variety .of combination in bimetaltypes and configurations as well as the manner of cou lin the o inforces together, may be employed td pe or'm I e com pensating actiondescribed and claimed herein.

lclaim:

l. A switch mechanism comprising: supportmeans, fixed and movablecontact means secured relative to said support means, anoperator meanssecured relative 7 said latch means being thermally responsive andhaving to this position swings the projection 9 against latch 34heatgenerating means, ambient temperature responsive means secured tosaid support means in space relation to said latch means and engagingsaid latch means to counteract the adverse torque developed in saidlatch means by changes in the ambient temperature,

said heat generating means being energized when said.

operator means is moved from said first position to said second positionto move said latch means out of engagement with said contact meanswhereby said contact means disengage.

2. A switch mechanism'comprising: support means, fixed andmovablecontact means secured relative to said support means, an operatormeans secured relative to said support means and having a first positionwherein said operator means causessaid contact means to engage eachother, and latch means which hold said contact means in engagement witheach other for a predetermined interval .of time after said. operatormeans-is moved from said first position to saidsecond position out ofengagement with said movable contact means, said latch means including abimetal blade secured at one of its two ends to said support means andhaving heat generating means, a second bimetal element secured to saidsupport meansin space relation to said bimetal blade and oriented sothat its ambient temperature responsive flexure engages and opposes thatof said bimetal blade and thereby counteracts the adverse forcesdeveloped in said bimetal blade by changes in the ambient temperature,said heat generating means being energized when said operator means ismoved from said first position to said second position to move saidlatch means out of engagement with said contact means whereby saidcontact means disengage.

3. The switch as set forth in claim I wherein said operator means has athird position, said second position being between said first positionand said third position, said operator means engaging said latch meanswhen said-operator means is in said third-posi-

1. A switch mechanism comprising: support means, fixed and movablecontact means secured relative to said support means, an operator meanssecured relative to said support means and having a first positionwherein said operator means causes said contact means to engage eachother, and latch means which hold said contact means in engagement witheach other for a predetermined interval of time after said operator mansis moved from said first position to a second position out of engagementwith said movable contact means, said latch means being thermallyresponsive and having heat generating means, ambient temperatureresponsive means secured to said support means in space relation to saidlatch means and engaging said latch means to counteract the adversetorque developed in said latch means by changes in the ambienttemperature, said heat generating means being energized when saidoperator means is moved from said first position to said second positionto move said latch means out Of engagement with said contact meanswhereby said contact means disengage.
 2. A switch mechanism comprising:support means, fixed and movable contact means secured relative to saidsupport means, an operator means secured relative to said support meansand having a first position wherein said operator means causes saidcontact means to engage each other, and latch means which hold saidcontact means in engagement with each other for a predetermined intervalof time after said operator means is moved from said first position tosaid second position out of engagement with said movable contact means,said latch means including a bimetal blade secured at one of its twoends to said support means and having heat generating means, a secondbimetal element secured to said support means in space relation to saidbimetal blade and oriented so that its ambient temperature responsiveflexure engages and opposes that of said bimetal blade and therebycounteracts the adverse forces developed in said bimetal blade bychanges in the ambient temperature, said heat generating means beingenergized when said operator means is moved from said first position tosaid second position to move said latch means out of engagement withsaid contact means whereby said contact means disengage.
 3. The switchas set forth in claim 1 wherein said operator means has a thirdposition, said second position being between said first position andsaid third position, said operator means engaging said latch means whensaid operator means is in said third position to displace said latchmeans from the path of movement of said movable contact means to permitsaid contact means to return to the open circuit position without thedelay interval.